#include <fstream>
#include <math.h>
using namespace std;
int main(){
ifstream fin;
ofstream fout;
fin.open("prim.in");
fout.open("prim.out");
short a[2000001];
long nr,n, i,j;
fin>>n;
for (i=2;i<=n;i++)
  a[i]=1;
for (i=2;i<=sqrt(n);i++)
  for (j=2;j<=n/i;j++)
     a[i*j]=0;
for (nr=0,i=2;i<=n;i++)
  if (a[i]) nr++;
fout<<nr;
fin.close();
fout.close();
return 0;
}